The present invention is broadly related to integrating analog-to-digital converters. More particularly, the present invention is directed to precision analog-to-digital converters for converting an analog accelerometer output signal to a digital representation thereof, useful for navigational systems.
As is well understood in the navigational arts, a navigational computer requires the information of three (3) accelerometers and three (3) gyroscopes providing acceleration and rotation information along and about three (3) orthogonal coordinate axes. A navigation system processor takes this information and solves navigation system equations in order to give precise global position information. Such systems are commonly employed on both military and commercial aircraft and water craft, and including such applications as submarines and space vehicles.
A navigation system processor, employing, e.g. a computer, microprocessors, or the like, requires the gyroscopic and acceleration information be in digital signal form. Accordingly, employment of an analog accelerometer commonly known in the art, generally produces an output that must be converted to a digital signal form, i.e., a digital representation of an analog quantity. Commonly, the analog accelerometer is converted by the employment of a precision integrating analog-to-digital converter and provides a digital number representation where each digital number increment represent a velocity increment--i.e., integrated acceleration.
In order to provide precision navigational systems, the ambient temperature of the components must be taken into consideration in order to provide precision navigation data. Therefore, employment of an analog accelerometer requires compensation and/or correction due to variations in the accelerometer's analog output signal as a function of accelerometer temperature.
Accordingly, the integrating analog-to-digital converter is designed with precision components having minimal temperature coefficients in order to enhance precision digital information representative of the acceleration sensed by the accelerometer. Secondly, systems of the prior art employ a temperature sensor for sensing the temperature of the accelerometer. Commonly, either the sensor manufacturer or user will characterize the accelerometer as a function of the sensor ambient temperature. Usually the characterization is in the form of accelerometer scale factor and bias as a polynomial function of temperature. In turn, this characterization information is utilized by the navigation processor to correct digital information from the integrating analog-to-digital converter in order to provide compensated and/or corrected navigation information.
Because the precision of the navigation system is dependent upon both the accelerometer and the integrating analog-to-digital converter, temperature characterization alone of the accelerometer is insufficient for a high precision navigation system information. For enhanced performance, temperature characterization of the integrating analog-to-digital converter is necessitated to provide more precise navigation system information.